The process for receiving the favor of the Supreme Personality of Godhead is described here. Yat-pāda-paṅkaja-palāśa-vilāsa-bhaktyā (SB 4.22.39). Simply by thinking of Kṛṣṇa, one can attain Him very easily. Kṛṣṇa is also described as having His lotus feet always within the hearts of His devotees (bhagavān bhakta-hṛdi sthitaḥ). In the case of Aghāsura, one may argue that he was not a devotee. The answer to this is that he thought of Kṛṣṇa for a moment with devotion. Bhaktyāham ekayā grāhyaḥ. Without devotion, one cannot think of Kṛṣṇa; and, conversely, whenever one thinks of Kṛṣṇa, one undoubtedly has devotion. Although Aghāsura's purpose was to kill Kṛṣṇa, for a moment Aghāsura thought of Kṛṣṇa with devotion, and Kṛṣṇa and His associates wanted to sport within Aghāsura's mouth. Similarly, Pūtanā wanted to kill Kṛṣṇa by poisoning Him, but Kṛṣṇa took her as His mother because He had accepted the milk of her breast. Svalpam apy asya dharmasya trāyate mahato bhayāt (BG 2.40). Especially when Kṛṣṇa appears as an avatāra, anyone who thinks of Kṛṣṇa in His different incarnations (rāmādi-mūrtiṣu kalā-niyamena tiṣṭhan (BS 5.39)), and especially in His original form as Kṛṣṇa, attains salvation. There are many instances of this, and among them is Aghāsura, who attained the salvation of sārūpya-mukti. Therefore the process is satataṁ kīrtayanto māṁ yatantaś ca dṛḍha-vratāḥ (BG 9.14). Those who are devotees always engage in glorifying Kṛṣṇa. Advaitam acyutam anādim ananta-rūpam: (BS 5.33) when we speak of Kṛṣṇa, we refer to all His avatāras, such as Kṛṣṇa, Govinda, Nārāyaṇa, Viṣṇu, Lord Caitanya, Kṛṣṇa-Balarāma and Śyāmasundara. One who always thinks of Kṛṣṇa must attain vimukti, special salvation as the Lord's personal associate, not necessarily in Vṛndāvana, but at least in Vaikuṇṭha. This is called sārūpya-mukti.
Especially when Krsna appears as an avatara, anyone who thinks of Krsna in His different incarnations, and especially in His original form as Krsna, attains salvation. There are many instances of this, & among them is Aghasura, who attained sarupya-mukti
SB Canto 10.1 to 10.13
Especially when Kṛṣṇa appears as an avatāra, anyone who thinks of Kṛṣṇa in His different incarnations (rāmādi-mūrtiṣu kalā-niyamena tiṣṭhan (BS 5.39)), and especially in His original form as Kṛṣṇa, attains salvation. There are many instances of this, and among them is Aghāsura, who attained the salvation of sārūpya-mukti.
If even only once or even by force one brings the form of the Supreme Personality of Godhead into one's mind, one can attain the supreme salvation by the mercy of Kṛṣṇa, as did Aghāsura. What then is to be said of those whose hearts the Supreme Personality of Godhead enters when He appears as an incarnation, or those who always think of the lotus feet of the Lord, who is the source of transcendental bliss for all living entities and by whom all illusion is completely removed?